Bodily flow measuring system

ABSTRACT

A system of measuring the flow of a human or animal bodily action or fluid along or through a bodily flow conduit using two or more sensor means located on the body and along or around the path of the conduit is described. Bodily fluids whose flow is measurable by the present invention include blood, semen and urine. The present invention is a non-invasive way of measuring the flow of a bodily action or fluid along or through a conduit, such as pulse wave velocity. Pulse wave velocity in the brachial artery can provide an indication of vessel wall quality or stiffness, which in turn, can be used to indicate how an individual&#39;s vascular system is ageing. Disorders such as stenosis and complete occlusion can be diagnosed by accurate measurement of pulse wave velocity.

The present invention relates to a system and method for measuring theflow of bodily fluids such as blood or semen, or action such as pulsewave velocity, and apparatus and means therefor.

Current research suggests that 850 people with hypertension have to betreated for 1 year to prevent 1 stroke. Anything that would allow ageneral practitioner in the primary health care setting to be morespecific in preventing vascular disease would be of benefit.

A review of the literature suggests that pulse wave velocity (PWV) couldbe used as a means of indirectly assessing vessel wall stiffness. Vesselwall stiffness has been found to be an indicator of sub-clinicalatherosclerosis in clinical hypertension, and that the presence ofsub-clinical atherosclerosis predicts an increased risk of overtvascular disease. Evaluation of the arterial wall elasticity is apossible way of diagnosing the onset of vascular impairment at an earlystage and could facilitate the effective treatment of this problem.

Pulse wave velocity measurement is well established in physiologicalresearch and has been useful in measuring the effects of diabetes andhypertension on blood vessels. Some modern cardiovascular drugs havebeen shown to influence PWV and it may be that, in the future,adjustment of PWV by therapeutic means could reduce the incidence ofvascular disease.

Following each cardiac contraction, a pressure wave is generated in theaorta. The radial stress applied to a arterial wall creates a localdeformation which propagates from the heart to peripheral sites. As PWVdepends on the elastic properties of the arterial wall, it is widelyused as an index in healthy subjects or in patients suffering formvarious diseases. A high wall stiffness is a condition which persists atall times of the day regardless of activity or mental state. Thesufferer may not feel ill but may still be at risk of developing heartdisease and/or a disturbance of the circulation. The longer thiscondition goes undetected the greater the risk that one of theaforementioned diseases could result in death.

Currently there is research into pulse wave velocity measuring systemsand into the development of devices utilising a range of techniquesincluding: Doppler ultra-sound techniques; fibre optic measurementsystems and electrical impedance measurements. However, the devicespresently being used have disadvantages including their high errormargin. Ultra-sonic methods can only be done in hospital, and themeasurements have aberrations caused by the distortion of the waves asthey pass through body tissue.

There is need therefore for a low cost, non-invasive method to measurePWV.

According to one aspect of the present invention, there is provided asystem of measuring the flow of a human or animal bodily action or fluidalong or through a bodily flow conduit using two or more sensor meanslocated on the body along or around the path of the conduit.

The present invention equally provides a method for making suchmeasurements.

Bodily actions include pulse waves. Thus, in one embodiment of thepresent invention, there is provided a pulse wave velocity measuringsystem comprising two or more pressure sensor means, preferably arrangedalong a support means, such that at least two of the sensor means arelocatable over a bodily fluid conduit such as an artery of a human oranimal body, and a means to transfer signals from the sensor means to asignal processing means adapted to calculate the pulse wave velocitybetween the sensors.

Bodily fluids whose flow is measurable by the present invention includeblood, semen and urine. Blood flow through a major artery or areas suchas the carotids, aorta and distal arteries e.g. in the legs, ismeasurable. The speed or velocity of seminal fluid during ejaculation isalso measurable.

In all circumstances of bodily actions or fluids passing along orthrough a conduit, there is an electrical and/or mechanical indicator orsignal, such as an electrical or muscular discharge, differential ordeformation. It is such signals that can be detected by sensor means.

The electrical or mechanical signal may be directly associated with theconduit, e.g. a pressure measurement thereof. However, the signal mayalso or alternatively be associated with another part of the body, e.g.a myocardial discharge, which nevertheless is indicative of an actioncausing flow, e.g. of a pulse wave.

Because the sensors are a known distance apart, recognition of thesignals for e.g. a pressure wave (caused by deformation of the arterialwall as blood passes therealong) by the sensors can be calculatedagainst the known distance to provide a velocity measurement. Anacceleration measurement could also be provided. The system isnon-invasive by relying on the detection of a bodily signal. Manyelectrical signals can relatively easily be detected. Mechanical signalscan be based on the mechanical relation between skin movement and thesensors located thereon.

The sensors can be electrodes, or e.g. piezoelectric sensors adapted toconvert mechanical stress or strain into proportionate electricalenergy. One major benefit of piezoelectric film is its low acousticimpedance when close to human tissue. This therefore permits moreefficient transduction of acoustic signals in tissue. Piezoelectricfilms also have a high degree of elastic resilience, and consequently alow mechanical quality factor (Q).

Other sensors include liquid strain gauges, such as conductive oils/gelsand new forms of carbon loaded liquids and electrolyte (e.g. Na Cl)gauges, as well as conductive polymer wires.

Indium: Galium In/Ga is also a suitable strain gauge sensor forbiomedical sensors because it is liquid at room temperature, safe,inexpensive and its sensor properties are within the required range forbio-fluid pulse monitoring. When In/Ga is inserted into a flexiblepolymer tube and metal electrodes are attached at either end, theresistive or conductive properties will vary with strain. In/Ga sensorshave demonstrated that when applied to this fluid monitoring that theycan provide excellent measurement properties, such as conformalattachment, fast response times, good resolution and suitable mechanicalattributes.

Preferably, the mechanical sensors are polyvinylidene fluoride (PVDF)sensors. PVDF is resistant to most chemical substances and is notsensitive to radiation.

Different sensors would be suitable for different positions, signals, orparts of the body, depending on the degree of sensitivity required,signal-to-noise ratio, locational difficulties, etc. Preferably, thesensor means wholly or substantially conform to the body area on whichthey are located. The part of the sensor means interfacing with the bodycould be a flexible polymeric material.

The measuring method and system of the present invention may compriseany number of sensor means. In one embodiment of the present invention,the sensors may be wholly or substantially longitudinally aligned so asto be locatable along the path of the conduit such as an artery. In analternative embodiment, a number of sensors may be strategically locatedacross an area, possibly in rows, so as to be located across an area ofthe human or animal body. Measurements can be taken from those sensorsproviding the strongest signals, and therefore expectedly located abovethe path of e.g. the largest and strongest artery. Accurate location ofthe sensors or means to support the sensors may then be less essential.

The system of the present invention may also have one sensor means,being pressure or electrical such as an ECG electrode, located onanother part of a subject to provide a timing start e.g. on the chestfor arterial blood flow and/or a pulse wave, to a distal sensor means.

The system could also be combined with other medical appliances such asa blood pressure reading means.

The sensor means may be arranged along a support means. The supportmeans may have any suitable shape, size and design such that it islocatable, fittable and preferably attachable on or around a part of ahuman or animal body. The support means may be integral with orseparable from one or more of the sensor means. The support means maycomprise one or more separable portions, each portion optionally havingone or more sensor means therewith.

In one preferred embodiment of the present invention, the support meanscomprises a collar or a cuff adapted to be locatable around an elongateportion of a human or animal body such as an arm.

Also preferably, the support means includes means to attach or fititself around or onto the human or animal body. The support means mayinclude one or more fastening means such as VELCRO (RTM). The supportmeans may also include means to adjust its fittment or attachment to thehuman or animal body such as an eternal or internal inflatable bag.

The support means may be wholly or substantially rigid, or be wholly orsubstantially flexible, whilst also possibly including a wholly orsubstantially rigid frame, or a rigid frame piece. The support means mayinclude a reference means or portion, adapted to reference the supportmeans to a part of the human or animal body, e.g. the thumb, wrist orelbow, to ensure that the sensors are wholly or substantiallyrelocatable when repeat or comparative measurements are desired ornecessary.

The support means may also comprise one or more parts adapted to conjointhe support means to the human or animal body, and one or more partsadapted to support the sensor means to allow their location andsensitive movement on the human or animal body.

In one preferred embodiment of the present invention, the support meanscomprises one or more pockets arranged in a wholly or substantiallyrigid frame, which pocket(s) support a sensor means to allow mechanicalconjoining of the sensor means to the skin of the human or animal body.

Thus, according to a second aspect of the present invention, there isprovided a support means for two or more sensor means for measuring theflow of a human or animal bodily action or fluid along or through aconduit, such as pulsed wave velocity, comprising a wholly orsubstantially rigid frame and a pocket means for each sensor, the pocketmeans adapted to support a sensor means and allow sensitive movementthereof.

The means to transfer signals from the measuring system or method of thepresent invention includes any suitable signal transfer means which canbe directly or remotely connected to a signal processing means. Thetransfer signal means could simply be a wire lead for connecting into asignal processing means such as a computer or other analysing unit ormeans. The signal transfer means could also be adapted to transmit asignal to a separate or remote signal processing unit, either directlyor via other telemetry means such as a telephone network.

According to a particular embodiment of the present invention, there isprovided a method of measuring pulsed wave velocity comprising the stepsof:

locating two or more pressure sensor means wholly or substantially alongthe path of a bodily fluid conduit of a human or animal body,

measuring the signals from the sensors based on deformation of theconduit wall as fluid passes therethrough, and

calculating pulse wave velocity from the timing of the signals anddistance between the sensors.

Preferably, the pressure sensor means are piezoelectric sensors in asupport means.

Embodiments of the present invention will now be described by way ofexample only and with reference to the accompanying diagrammaticdrawings in which:

FIG. 1 is an arterial pressure wave form;

FIGS. 2 a and b are perspective and end views respectively of a pulsedwave velocity measuring system according to one embodiment of thepresent invention;

FIG. 3 is a schematic drawing of a human arm showing possible locationof the measuring system of FIG. 2 along said arm;

FIG. 4 a is a pulse wave velocity measuring system according to a secondembodiment of the present invention.

FIG. 4 b is a sensor mount for a sensor means useable for the presentinvention;

FIG. 4 c is a sample In/Ga sensor arrangement;

FIG. 5 is a schematic drawing of two pressure sensor means andassociated signal processing means usable with the present invention;

FIGS. 6 a–d are graphs of pressure wave forms of Subjects 1–4 measuredaccording to the present invention;

FIGS. 7 a–d are bivariate scatterplots based on multiple regression ofthe pulsed wave velocity systolic pressure measurements from the graphsof FIGS. 6 a–d; and

FIG. 8 is a human ejaculation spectrum.

Following each cardiac contraction, fresh blood is pumped throughout thebody. This generates a pressure wave in the aorta. Pulsed wave velocityis the velocity of the pulse pressure wave-form. It depends on theartery and the condition of the person.

The radial stress applied on the arterial wall by the pressure wavecreates a local defamation which propagates from the heart to peripheralsites. The pulse pressure wave-form results from the ejection of bloodfrom the left ventricle and moves with a velocity much greater (about 5to 10 m/s) than the forward movement of the blood itself.

The definition equation is:PWV=k·√[V·ΔP/ΔV][where: PWV: Pulse Wave Velocity; k: constant; V: Initial Vessel Volume;ΔP:Pressure Delta; ΔV:Vessel Volume Delta;]

With increased vessel wall stiffness (decreased compliance), ΔVdecreases and pulse wave velocity increases. With increased bloodpressure, the arterial walls are stretched more strongly and pulse wavevelocity increases. Accordingly, for a fixed vessel distance, as the PWVincreases the blood pressure increases as well.

As pressure waves travel form the aorta and large arteries to thenarrower, less compliant distal arteries, they travel at a greaterspeed. A hardened artery will yield a higher PWV due to the reducedresistance exerted to the pulse wave, and the wave will be reflectedwith greater intensity.

FIG. 1 shows a theoretical in vivo arterial pressure wave form overtime. This sequence shows a pressure pulse passing an observation pointon the arterial tree. The symptomatic anomalies of the trace areidentified as the late systolic peak and the dicrotic notch. Wavereflections can be quantified as the ratio of the height of the latesystolic peak to the total height of the arterial pulse wave. Traveltime of a reflective wave can be calculated from the foot of thepressure wave to the foot of the late systolic peak.

FIGS. 2 a and b show a first pulse wave velocity measuring systemaccording to the present invention. It comprises two sensor means 2, 4located within a support means 6. The support means 6 comprises a whollyor substantially rigid tubular outer frame cuff 8, longitudinally hinged10 and longitudinally separable opposite the hinge 12 (not shown).

Within the outer frame 8 the support means 6 has a coaxial flexible bag14. The bag 14 is inflatable by any suitable means such as a hand pump.The sensors 2, 4 are located on the internal side of the bag 14. Leads16 extend from each sensor 2, 4 into a single signal transfer means 18which could be directly connectable into a signal processing means suchas a computer or other analysis unit (not shown).

FIG. 3 is a schematic drawing of two PVDF sensors 20 adapted to detectthe pulse signal at two designated positions on a human or animal body.The sensors 20 are connected to an analogue processing circuit 22 toconvert the charge generated by the sensors 20 into a voltage signal, toamplify the small signal, and to filter out any undesired frequencies.From there, the signal is transferred to a data acquisition board 24 todigitise the acquired signal, and then transferred to a computer 26having relevant software to perform data logging, digital signalprocessing, computation of pulsed wave velocity, and analysis on thepressure wave profile.

FIG. 4 a shows a second pulse wave velocity measuring system. The systemhas two rows of sensor means 40 supported near the ends of an elongateflexible cuff 42. The cuff 42 can be located around the arm of a humansubject (not shown), and fasteners 44 provide fixing of the cuff 42around the arm.

The cuff 42 could include a rigid “spine” piece 45 (shown in dottedline) to assist comparative or reproducible locality of the cuff 42.That is, by ensuring that one end of the spine piece 45 always abuts theinner elbow between the upper and lower arms, it can be considered thatthe sensor means are located in the same general position for eachmeasurement.

The sensors 40 are arranged so that at least one of the sensors 40 ineach row will be located above an artery. The sensors 40 are connectedby a lead 46 to a signal processing unit 48, which can analyse thesignals from all the sensors and select the strongest or biggest signalfrom each row of sensors 40. Also connected to the processing unit 48 isan ECG electrode 50 attachable to the front of the chest of the subject,which can detect the initiation of the pulse wave at the heart, and soprovide a timing or timed start of the pulse wave. This can beconsidered with the time taken for the pulse wave to get from the heartto the cuff sensors 40. The cuff pressure should be below the diastolicpressure.

FIG. 4 b shows a sensor mount 52 for holding a PVDF sensor means 54. Themount 52 has an adjustable screw 56 acting on a plate 58, beneath whichthe sensor means 54 is locatable, with its edges held by clips 59 of themount 52. Adjusting the screw 56 serves to adjust the height of thesensor means 54 relative to a conjoined cuff 60, and so optimise skincontact.

FIG. 4 c shows a schematic view of the arrangement for an Indium/Galiumsensor 60 having metal electrode heads 62, and an intermediate flexibletube 64 of Indium/Galium.

FIG. 5 is a schematic drawing of a human arm on which the brachialartery is highlighted. For the experimental data hereinafter, a pulsewave velocity measuring system was located around subjects and the twosensors of said measuring system were located either as shown in FIG. 4a or FIG. 5.

In the experimental data hereinafter, Sensor A was an LTD seriespiezoelectric sensor generally having a protective coating piezo filmand polyester laminate. Sensor B was a DT series of piezoelectric filmelement sensor having outer protective coatings, and a central piezofilm sandwiched between metalization layers. Both these forms of sensorsare PVDF sensors. The distance between the sensors was measured andrecorded into the signal processing means.

Experimental Data

Subject Sex Age Fitness 1 Male Mid 20's Moderate 2 Male Mid 20'sAthletic 3 Male Mid 20's Moderate 4 Male Mid 20's Athletic

FIGS. 6 a–d are graphs of pressure wave forms conducted on Subjects 1–4respectively.

FIGS. 7 a–d depict the findings of the linear regression of theunscreened PWV data of FIGS. 6 a–d respectively. Those results whichreside in the vacinity of the regression line in FIGS. 7 a–d reflect thesuccessful prediction of PWV values using the linear regression formula.

Analysis of this information also indicates that there is no linearrelationship between PWV and systolic and diastolic pressures. Theregression line being almost horizontal in FIGS. 7 a–d also implies thatthere is no direct relationship between PWV and blood pressure. Thetable below summarises the results of the preliminary clinical trialsregarding PWV and blood pressure (artificially increased via exercise).

Strength of Systolic-PWV PWV (m/s) PWV (m/s) Subject Relationship MeanStd. Dev 1 −0.0576 6.895 0.793 2 0.0001 6.851 0.767 3 0.0054 6.754 0.6154 −0.0157 6.819 0.650

The inference from these findings is that PWV remains consistent asblood pressure is increased through exercise.

The above data confirms that there was no significant relationshipbetween PWV and blood pressure (“artificially” manipulated viaexercise). PWV is a more reliable diagnostic tool in evaluatinghypertension in a subject because blood pressure can be easilymanipulated via exercise or indeed stress and can therefore oftenindicate erroneous values in the clinical assessment of a subject. PWVprovides a more robust indicator in the clinical assessment of asubject.

Results here also indicated that PWV remains constant when a cuff isplaced on the upper arm and remains inflated at sub-diastolic levels.However, once the cuff is inflated above the diastolic level, PWV willbe greatly reduced and became more variant. This result is in agreementwith traditional usage of cuff for blood measurement. As the cuff isinflated to occlude the artery, the pressure flow dynamics in thebrachial artery becomes occluded when the cuff pressure exceeds thesystolic level. As PWV is based on the detection of the blood pressurepulse, the turbulent dynamics caused by partial occlusion would accountfor the high variance in PWV above diastolic.

The obtained PWV values in the experiments were between 5.1 m/s and 11.2m/s and the reproducibility varied between 9.11% and 11.50%. Althoughthese values were not compared with an external reference system, theliterature suggests PWV should be between 5 m/s and 15 m/s for subjectswith similar age and health background. When analysing the data at the5% confidence level, the percentage error of the mean was typically ≅3%,which suggests that the PWV data has a good central tendency. Again,this reflects the robust nature of PWV, and the reliability of the dataacquired via this system.

FIG. 8 shows a profile of sperm load and events against time duringejaculation. The area under the graph is sperm load. The spectrumconfirms the use of the present invention to provide a profile suitablefor medical interpretation.

The present invention is a non-invasive way of measuring the flow of abodily action or fluid along or through a conduit, such as pulse wavevelocity. Pulse wave velocity in the brachial artery can provide anindication of vessel wall quality or stiffness, which in turn, can beused to indicate how an individual's vascular system is ageing.Disorders such as stenosis and complete occlusion can be diagnosed byaccurate measurement of pulse wave velocity.

The present invention provides apparatus and method for simple andnon-invasive measurement of the flow of a bodily action or fluid alongor through a conduit of any patient or subject. Such data can easily becompared with ‘normal’ or ‘typical’ subject data for immediate analysisand diagnosis by a medical practitioner. Such data could also be relayedto a location using known telemetry should the subject be remote fromthe signal processing means.

1. A system of measuring the pulse wave velocity of a human or animalbodily action or fluid along or through a bodily flow conduit comprisingtwo or more sensor means capable of substantially conforming to a bodyand detecting electrical signals, the sensor means located at least 2centimeters apart on the body along or around the path of the conduit, asupport means to apply a pressure below the diastolic pressure in theconduit wherein the sensor means are arranged in or on the supportmeans, a signal processing means adapted to calculate the velocitybetween the sensor means, and means to transfer signals from the sensormeans to the signal processing means.
 2. A system as claimed in claim 1wherein the bodily action is a pulse wave or pressure profile.
 3. Asystem as claimed in claim 1 wherein the bodily fluid is blood, semen orurine.
 4. A system as claimed in claim 1 wherein one or more of thesensor means measures a direct electrical and/or mechanical signal fromthe conduit.
 5. A system as claimed in claim 1 wherein one or more ofthe sensor means measures an indirect electrical and/or mechanicalsignal from a conduit.
 6. A system as claimed in claim 1 wherein one ormore of the sensor means is selected from the group consisting ofelectrodes, liquid strain gauges, conductive polymer wires, mechanicalsensors and Indium/Gallium sensors.
 7. A system as claimed in claim 6wherein the sensor means are piezoelectric sensors, polyvinylidinefluoride sensors or Indium/Gallium sensors.
 8. A system as claimed inclaim 1 wherein the sensor means wholly or substantially conform to theshape of the body on which they are located.
 9. A system as claimed inclaim 1 wherein the part of the sensor means interfacing with the bodyis a flexible polymeric material.
 10. A system as claimed in claim 1wherein the sensor means are wholly or substantially longitudinallyaligned along the path of the conduit.
 11. A system as claimed in claim1 wherein the sensors are located in rows across an area of the human oranimal body under which the conduit passes.
 12. A system as claimed inclaim 11, wherein the signal processing means analyzes the signals fromthe sensor means and selects at least one signal from each row of sensormeans.
 13. A system as claimed in claim 1 wherein the sensor means areintegral with the support means.
 14. A system as claimed in claim 1wherein the sensor means are separable from the support means.
 15. Asystem as claimed in claim 1 wherein the support means comprises acollar or a cuff adapted to be locatable onto or around an elongateportion of a human or animal body.
 16. A system as claimed in claim 1wherein the support means includes means to attach or fit itself onto oraround the human or animal body.
 17. A system as claimed in claim 1wherein the support means includes a reference means or portion adaptedto reference the support means to a part of the human or animal body.18. A system as claimed in claim 1 wherein the support means comprisesone or more pockets, which pocket supports a sensor means.
 19. A systemas claimed in claim 1 wherein one or more sensor means are additionallylocated at a distal location on the human or animal body.
 20. A systemas claimed in claim 19, wherein the bodily action is a pulse wave orpressure profile and wherein the one or more distally located sensormeans detects an initiation of the pulse wave or pressure profilethereby providing a timed start of the pulse wave or pressure profile.21. A system as claimed in claim 1 for measuring the pulse wave velocityalong a human artery.
 22. A system as claimed in claim 1 for measuringthe velocity and/or volume of seminal fluid during ejaculation.
 23. Asystem as claimed in claim 1 for measuring a pressure, volume orevent-timing occurring along or through the conduit.
 24. A method ofmeasuring the flow of a human or animal bodily action or fluid along orthrough a bodily flow conduit, which method comprises using the systemas claimed in claim
 1. 25. A support means for two or more sensor meansfor measuring the flow of a human or animal bodily action or fluid alongor through a conduit as described in claim 1, comprising a frame and asupport for each sensor means adapted to allow sensitive movementthereof.
 26. A support means as claimed in claim 25, wherein the frameis wholly or substantially rigid.
 27. A system as claimed in claim 1,wherein the support means comprises an adjustable fastener; and a framein communication with the adjustable fastener.
 28. A method of measuringthe pulse wave velocity of a human or animal bodily action or fluidalong or through a bodily flow conduit, the method comprising the stepsof: locating two or more sensor means at least 2 centimeters apartwholly or substantially along the path of the conduit of a human oranimal body, the sensor means capable of substantially conforming to thebody and detecting electrical signals, and locating support means on thebody to apply a pressure below the diastolic pressure in the conduit;measuring the signals from the sensors based on deformation of theconduit wall as fluid passes therethrough; and calculating the pulsewave velocity from the timing of the signals and distance between thesensors.
 29. A method as claimed in claim 28 wherein the sensor meansare piezoelectric sensors in the support means.
 30. A method as claimedin claim 28, wherein the sensor means are located in rows furthercomprising analyzing the signals from the sensor means; and selecting atleast one signal from each row of sensor means.
 31. A method as claimedin claim 28, wherein the bodily action is a pulse wave or pressureprofile further comprising detecting an initiation of the pulse wave orpressure profile; and providing a timed start of the pulse wave orpressure profile.